1. Field of the Invention
This invention relates to electrical devices comprising enclosures which are sealed except for one or more small vents, and from which gas must be vented during use. The invention is particularly concerned with circuit protection devices in which one or more PTC conductive polymer elements are positioned within an enclosure.
2. Introduction to the Invention
In recent years much progress has been made in the design, manufacture and use of circuit protection devices containing PTC conductive polymer devices. Reference may be made for example to U.S. Pat. Nos. 4,237,441, 4,238,812, 4,255,698, 4,315,237, 4,317,027, 4,352,083, 4,413,301, 4,481,498 and 4,450,496 and to copending commonly assigned U.S. patent application Ser. Nos. 524,482, 628,945, 711,790, 711,907, 711,908, 711,909 and 711,910. The disclosure of each of these patents and patent applications is incorporated herein by reference.
In many circumstances, one or more PTC conductive polymer circuit protection devices are placed within a hollow enclosure. Since a conductive polymer element can, under certain circumstances, generate a substantial quantity of gas, it is necessary for the enclosure to comprise a vent or a thin section which will shatter and become a vent before the internal gas pressure becomes excessive.